Metallurgy of tin



Aug. 26, 1924. 1,506,053

C. G. FlNK METALLURGY OF TIN Filed March 17, 1921 Patented Aug. 26, 1924.

UNITED STATES PATENT OFFICE.

COLIN 6. mx, or YONKERS, NEW YORK, ASSIGNOR '10 GUGGENHEIM BROTHERS, A ooran'rnnnsnn', OF new xonx, N. x.

METALLUBGY OF TIN.

Application and larch 17, 1921. Serial No.- 452,951.

processes for the recovery of tin from tincontaining materials. More particularly, the invention relates to the recovery of tin from tin oxide ores, such as native or roasted tin ores or concentrates, or other appropriate tin-containing materials. The invention has for its object the provision of certain improvements in the metallurgy of tin, and, in particular, contemplates the provision of an improved method of recovering tin from appropriate tin-containing materials.

It has heretofore been the general prac tics in tin metallurgy to smelt tin ores, or other appropriate tin-containing materials in a reverberatory or shaft furnace employin a solid carbonaceous material, such as co e, as the reducing agent. In these heretofore customary processes, the reduction .of the tin compounds is brought about by carbon monoxide gas produced by the union of the carbonaceous material of the charge with air blown into or otherwise appropriately brought into contact with the charge. The formation of carbon monoxide by the reaction between solid carbonaceous material, such as coke, and air, does not readily take place at temperatures below about 1100 (1., and it is therefore necessary in smelting tin compounds with solid carbonaceous material to heat the charge to a temperature above 1100 C. in order to effect the necessary formation of carbonmonoxide gas for the reduction of. the tin compounds. Thus, in the heretofore customary reverberatory furnace practice, the charge, consisting, for example, of a native oxide or a roasted tin ore and coke and generally all appropriate fluxing agent, is brought to a temperature above 1100 C. so as to form, by the combustion of the coke, the carbon monoxide gas required for the reduction of the tin compounds to metallic tin. Substantially the same metallurgical reactions are involved in the smelting of tin-containing materials in accordance with the heretofore customary shaft furnace practice. However, 1t is usually the practice in smelting tin ores in a shaft furnace to supply the charge in alternate layers of coke and ore, in order to provide, by the combustion of the layers of coke and ore, in order to provide, by the combustionof the layers of coke as they progressively reach the active combustion zone of the furnace, a sufliciently high temperature to effect the production of carbon monoxide gas for the reduction of the tin compounds in the superposed layer of ore. In both the reverberatory and shaft furnace practice, it has heretofore been customary to include in the charge an appropriate fluxing agent, such as limestone, and two molten products, (1) reduced metallic tin and (2) slag, are appropriately withdrawn from the furnace.

The higher oxide of tin, unlike the higher oxides of copper and lead, is not readily dissociated by heat into the lower oxide. For example, in the smelting of copper and lead ores heat alone reduces the hi her oxides of copper or lead (CuO or PbO to lower oxides of copper or lead (Cu O or PbO). As a result of this dissociation of the higher oxides into the lower oxides and oxygen by heat alone, oxygen is liberated within the charge itself,'being in fact generated in situ, and this liberatedoxygen combines with the carbonaceous material of the. charge and forms carbon monoxide which effectively assists in the smelting operation. The oxygen thus liberated by the action of heat alone is more or less diffused throughout the body of the charge and insures, to a certain extent, the. presence of a considerable amount of oxygen within the charge itself. On this account, it is not difiicult in .copper and lead smelting to efi'ectia satisfactory diffusion within the body of the charge of suflicient oxygen for smelting purposes, since the charge is kept porous by the liberated oxygen and carbon monoxide and the externally derived air blowninto or otherwise appropriately brought into contact with the charge is effectively augmented by the oxygen liberated within the charge itself by the dissociation of the higher metal oxides into lower oxides and oxygen by the action ofheat alone.

In the smelting of tin ores, on the other hand, the natural diffusion of oxygen throughout the charge itself cannot be relied u on, because the higher oxide of tin (SnO is not readily dissociated b heat alone into the lower oxide (SnO? and ex gen, and at the temperatures usual y preva ing in the heretofore customary proc esses of tin smelting this dissociation does not take place to any appreciable extent. For this reason, in the smelting of tinores in the reveberatory furnace, the charge is not permeated to any appreciable extent with oxygen liberated from the compounds of tin by the action of heat alone. It is very important for the satisfactory smelting of tin ores that effective measures be employed to insure the necessary contact of the carbonaceous material of the charge with externally derived air for effecting the formation of the carbon monoxide gas required for the reduction of the tin compounds. In the reverberatory smeltin of tin ores, practically only the surface of the charge receives sufficient oxygen for the combustion of the carbonaceous material, and for this reason it is necessary to constantly rabble or work the charge in order to bring fresh material to the surface where the effective reaction is taking place. Moreover, at the relatively high temperature at which coke and air readily react to form carbon monoxide, namely, at temperatures of about 1100 0., there is a tendency in tin smelting for the charge to fuse before the tin compounds therein have been properly reduced, thereby rendering the surface of the charge still less pervious to the diffusion of gases and more effectively confining the reduction to the surface.

In the smelting of tin ores in shaft furnaces, in accordance with the heretofore customary practice, substantially the same objectionable conditions are encountered as in reverberatory smelting. The high temperature required for the formation of carbon monoxide tends to fuse the ore before the tin compounds therein have been properly reduced, thus rendering the ore less er vious to the effective diffusion of the car van monoxide gas. Thus, in both the heretofore customary reverberatory and shaft furnace smelting of tin ores, the first slag generally contains from 20% to 40% of tin due to the inability of the carbon monoxide gas to effectively reach all parts of the metalliferous material in the charge as well as to the great tendency of tin to combine with the gangue and the fiuxing agents in the charge at the relatively high temperature necessarily employed. I

The method of the present invention involves a radical departure from the heretofore customary processes of smelting tin ores. Thus, in accordance with the present invention, the tin-containing material is first subjected to a reducing treatment in the course of which the 00m unds of tin are reduced to metallic tin y a aseous reducing agent without fusion of t e nonmetallic or gangue constituents of the material and, i desired, without material glomeration of the reduced metal. e product of this reducin treatment is a mixture in which the re uced tin is more or less scattered throughout the non-metallic constituents of the original ore, and the next step in the method of the invention consists in effectin the separation of the metallic tin from t e aforementioned mixture. This separating step may be carried out in various ways, as will be fully described hereinafter. he aforementioned reducing treatment may be considered in the nature of a preparato step for the subsequent separation of t e metallic tin from the gangue constituents of the ore, and as a resu t of this reducing or preparatory treatment, there is obtained a mixture of metallic tin and gangue from which the metallic tin can be subsequently separated by various satisfactory procedures.

I have found that externally prepared gaseous reducing agents, such as hydrogen, carbon monoxide, or the like, effectively reduce stannic oxide to metallic tin at temperatures in the neighborhood of 550 C. to 900 C. At these relatively low temperatures fusion of the charge does not take place and the charge remains extremely permeable to the gaseous reducing agent. Moreover, these relatively low temperatures are Well above the melting temperature of metallic tin. Thus, in accordance with my present invention, the tin-containing material is heated to a temperature relatively low as compared with the heretofore customary practice in tin-smelting and a gaseous reducing agent is then blown into or otherwise appropriately brought into contact with the heated charge. Preferably, no fluxing agents are mixed with the charge, and the reducing operation merely involves heating the tin-containing material, forexample, roasted tin ore or concentrates, to a temperature of from 550 C. to 900 C. and subjectin the thus heated material to the action 0 a gaseous reducing agent, such as hydrogen, carbon monoxide, or a mixture thereof, the reducing agent being introduced into the charge in gaseous form.

In the practice of the invention. the tin ore, concentrate, or the like, preferably in a finely divided condition, is heated to a temperature of from 550 C. to 900 C., for example, by agas furnace or by electrical means. The heating or reducing chamber may advantageously take the form of a slightly inclined tube or chamber adapted to have the ore fed in at one end and the products of the reaction discharged at the gravity suitable .conve' means. inay be provideti other end, and provided with means for. the supply thereto of hydrogen or other appropriate gaseous reducing agent, and the removal' therefrom of the exhaust gases. Where the inclination of the reaction chamher is not sufiicient to-insure the passage of the orethrough the tube or chamber by or .rabbling or the tube or chamberfmaybe rotated to insure agitation of the, charge and uniform treatment thereof,-*'to-gether with gradual pr 'on of the charge through the-reaction c mher.

I The portions of the reaction chambercontacting with or exposed to the charge during the reaction should be made of a material adapted to withstand the corrosive efiects characteristic of the reaction. Thus, the reaction chamber may be made of or lined with suitable refractory material, such, for example, as an iron tube or cylinder lined with m esite. I prefer, however, to employ a tu or chamber composed of, or appropriately lined with, an alloy of iron and chromium containing not less than about of chromium. I have secured invention.

The tin ore or concentrate is heated in the reaction chamber or furnace to a suitable temperature, temperatures between 550 C. and 900 C. being satisfactory, and hydrogen or other appropriate gaseous reducing agent, is brought into contact therewith in a sufficient amount and for a suflicient period of time to insure reduction of the tin oxide. The selection of the best reducing temperature is of great importance for eflicient operation. It is well lmown that as a general rule the velocity of a chemical reaction. increases rapidly with the temperature. Accordingly, as far as the chemical reduction of tin oxide is concerned high temperatures, of 1000 C. and over, are to be preferred. However, aside from the fume losses. at high temperatures, I find that it is good practice to keep the charge porous and prevent fusion or slagging. For, as is pointed out herein, the quantity of tin con-.

centrates reduced per unit of time is dependent not directly upon the chemical reaction velocity but upon the diffusion velocity of the reducing gas and water vapor produced. It is readily appreciated that a redu cing gas such as hydrogen will pass through a fused charge;

will raise this point.

through a porous charge more rapidly than Accordingly, a temperature as little "below the slagging point of the gue as possible should be selected in or er to secure the best results. This slagging point varies from one lot of concentrates to the other, depending largely upon the relative amounts of silica, iron,

lime, etc, in the gangue. Tin concentrates rich'in tourmaline usually have a low 'slagging point; the addition of a little lime The reduction takes; place without difliculllizzly and results in the production of meta 'c tin more or less scattered throughout this finely divided gangue or non-metallic constituents of the original ore. At temperatures around 650? C. and higher, the

reduced metallic tin tends to run together or agglomerate, and may, under appropriate operating conditions, be withdrawn from the furnace in a liquid metallic state. At A lower temperatures, the reduced metallic tin remains more or less distributed throughout the charge in admixture with the gangue etc. The reduced metallic tin may, accordin 1y, be distributed throughout the work- 0 charge in a finely divided state, or may be somewhat-agglomerated and more or less porous, or may, to a greater or less extent,

be recovered from the furnace in a liquid metallic state and directly cast or solidified in ingots or in the form of. anodesv for use in electrolytic refining. N o particular precautions appear necessary at the end of the reducing treatment to prevent reoxidation of the metallic tin.

\Vhere the tin is in part agglomerated together inthe product discharged from the furnace, this product may be appropriately treated to remove or separate the gangue, to the desired extent, from the reduced tin. This separation may be brought about by heating the mixture of reduced metallic tin and gangue to temperatures of 1000 C. to 1200 (3., with or without the addition of fluxes. This heating may be carried out in any appropriate type of furnace, such, for example, as a crucible furnace, and the metallic tin will melt and collect in the bottom of the furnace or crucible and may be appropriately withdrawn therefrom and thus separated from the gangue originally ad mixed therewith. The separation of the gangue from the reduced metallic tin may also be effected by subjecting the mixed product of the reducing treatment to a grinding and hydraulic classifying operationor to other appropriate concentrating or classifying treatments. The desired separation of the reduced metallic tin from the gangue in the worked-off charge may h temperature to melt the reduced mehi ta lic tin, is centrifuged in an appropriate centrifugal apparatus, preferably eated to -maintain the metallic tin in a liquid or monoxide, or hydrocarbons, or containing two or all of said gaseous reagents, may be employed in the practice of the invention, and I merely mention by way of example, water gas, producer gas, illuminating gas, oil gas and hydrocarbon vapor or vapors as appropriate gaseous reducing agents for the practice of the invention. It will be understood by those skilled in the art that various hydrocarbon and similar compounds which are decomposed at the reaction temperature contemplated by the invention into volatile reducing agents may be employed as the source of the gaseous reducing agents for the purposes of the invention. Thus, methane, benzine, alcohol and the like may serve as the source of an appropriate gaseous reducing agent for the purposes of the invention.

When using ores containing metallic sulfides it is advantageous, though not absolutely essential, first to roast the ore so as to convert the metallic sulfides to metallic oxides, and then to subject the roasted ore,

- omizing in the amount of heat required, and

taking advantage of the hot reactive condition of the freshly roasted ore. The roasting operation may be effected in the same furnace in which the ore is to be subsequently reduced, or in a separate furnace from which the roasted ore is directly discharged into the reducing furnace. ore to the reducing furnace may be continuous where the furnace is provided with means for the continuous supply thereto of ore and the continuous discharge therefrom of the worked-off charge, or the feed to the reducing furnace may be intermittent and successive charges of ore subjected therein to the reducing treatment.

Any sulfur occurring in small amounts in native or raw oxide or oxidized ores, or any unoxidized sulfur remaining in a roasted sulfide ore, will be subjected to the reducing action of the hydrogen during .thereduction of the ore, with the resulting formation of hydrogen-sulfide. The addition of small amounts of chlorine or hydrochloric acid,

The feed of the for example, b mixing chlorine or hy drochloric aci gas with the hy rogen gas or by otherwise adding chlorine or hydrochloric acid to the ore, accelerates the removal of sulfur.

I prefer, in practicing the present invention, to add no fiuxing agent to the charge. By the improved process of the invention, the compounds of tin are reduced, at relatively low temperatures as compared with prior processes of tin smelting, without necessitating the fusion or slagging of the gangue constituents in the ore. In fact, one of the peculiar advantages of the process of the invention resides in the fact that only the reduced metallic tin is melted at the prevailing reaction temperatures, and the gangue material in the ore remains solid throughout the entire reducing operation. When smelting tin ores of comparatively low melting point for example, ores containing large percentages of. tourmaline, lime-stone (294.40%) may be added to the ore to counteract any tendency which the garligue of the ore may display to fuse or me t.

- As hereinbefore mentioned, the method of V the invention may advantageously be carried out as a continuous process, by supplying the ore to the furnace in a continuous or intermittent manner and similarly withdrawing the reduced tin and ore residue and by supplying the hydrogen, or other appropriate reducing gas, in a continuous and regulable manner. The gaseous reducin agent may advantageously be introduced near the discharge end of the furnace so that it comes in contact first with the reduced and partly reduced ore, thus insurin complete reduction. By proper supply an regulation of the supply of the gaseous reducing agent, substantially complete utilization of the reducing gas can be secured so that the gases discharged from the furnace will be made up of steam, carbon dioxide, and inert ases I preferfiiowever, to use an excess of hydrogen or other suitable reducing gas and to keep this gas in constant circulation allowing it to sweep over the char e at a comparatively rapid rate for examp c 40 cu. ft. per square foot of hearth per hour. As the gas leaves the furnace and before reentering it, the products of combustion, such as water, are preferably removed. I have found that the velocity of reduction is largely dependent upon the speed with which the water vapor (in the case of reduction by hydrogen) is removed. The velocity of reduction is proportional to the speed of the diffusion of the reducing gas through a film of water covering the tin oxide articles. The chemical reaction between tie tin oxide and hydrogen is com aratively rapid at temperatures of 600 and above.

A suitable apparatus for use in carrying out the invention is illustrated in the ac-1 nace tube 6 which may be constructed of any suitable material as hereinbefore suggested, but which is preferably made from an alloy of iron and chromium containing not less- ,than about 30% of chromium. The furnace tube may be heated by any suitable means, the electric heating element 7 bein shown by way of illustration. The finely dlvided material istsupplied to the furnace tube through an iii'let 8, and its movement through the tube is facilitated by a rabble 9 which is also constructed preferably of the iron chromium alloy. The rabble 9 is supported on a shaft 10 carried in suitable bearings at the ends of the tubeand driven through a gear 11 or the equivalent driving connection from a source of power.

The reducing gas, such as hydrogen, is supplied to the furnace tube througha ipe 12 connected to a source of supply, an as the hydrogen passes through the mass of material under treatment the reducing action hereinbefore described is carried on for the accomplishment of the intended purpose. The operation of the furnace may be such that reduced material is continuously or intermittently withdrawn therefrom, and this material may be delivered into a crucible 13 which is preferably heated by an electric are between electrodes 14 and 15, the latter being supplied with power through cables 16. Preferablya pipe 11 permits the introduction of a reducing gas such as hy drogen to the crucible to prevent oxidation of the contents. In the crucible the reduced tin separates and descends to the bottom from which it may be withdrawn through a tap 18. The, overlying slag may be withdrawn similarly through a tap 19.

The details- "of the structure described are merely illustrative of a possible form of apparatus. These details may be varied, and other means may be substituted for the furnace tube and crucible as hereinbefore set forth.

The reduced metallic tin, whether in a solid metallic state or admixed with the gangue constituents of the ore, is well adapted for electrolytic refining. When the tin runs out of the furnace. as metallic tin, this may be cast in the form of anodes and these anodes used in the electrolytic refining operation. Where the reduction is carried out at relatively low temperatures, so that the reduction product is porous, this product can be compressed and used in the electrolytic refining process without separation of the reduced tin from the gangue, or the reduction product can -be concentrated and the concentrate compressed and used as the anode in theelectrolytic process. Tin thus produced is well adapted for electrolytic refining'by the process of my a lication for Letters Patent of the United gliates, Serial No. 533,249: filed February 1', 1922' making use of an electrolyte containing a preponderatnig concentration of sulfate ions with respect to other anions present therein and a preponderating concentration ofions of a metal moreelectropositive than'tin with respect to other cations present'in the electrolyte.

I claim 1. A metallurgical process for the treatment of tin ores, concentrates, or other appropriate tin-containing material, which comprises heating the tin-containing material to an elevated temperature but below the fusing temperature of the non-metallic constituents of the charge, and bringing an externally prepared gaseous reducing agent into intimate contact with the thus-heated material and thereby reducing the compounds of tin to metallic tin without fusion of thenon-metallic constituents of said material.

2. A metallurgical process for the treatment of tin ores, concentrates or other appropriate tin-containing material, which comprlses heating the tin-containing material to a temperature of from 550 C. to 900 (1, and bringing an externally prepared gaseous reducing agent into intimate contact with the thus-heated material and thereby reducing the compounds of tin to metallic tin without fusion of the nonmetallic constituents of said material.

3. A metallurgical process for the treatment of tin ores, concentrates or other appropriate tin-containing material, which comprises heating the tin-containing material to a temperature of from 500 C. to 900 0., and bringing a gaseous reducing agent containing hydrogen gas and carbon monoxide gas into intimate contact with the thus-heated material andthereby reducing the compounds of tin to metallic tin without fusion of the non-metallic constituents of said material.

4. A metallurgical process for the treatment oftin ores, concentrates or other appropriate tin-containing material, which comprises heating the tin-containing material to a temperaturev of from 550 C. to 900 C., and bringing hydrogen gas into intimate contact with the thus-heated material and thereby reducing the compounds of tin to metallic tin without fusion of the non-metallic constituents of said material.

5. A metallurgical process for the treatment of tin ores,concentrates, or other appropriate tin-containing material, which comprises heating the tin-containing material, which comprises heating t e tincontaining material to an elevated temperture but below the fusing temperature of the non-metallic constituents of the charge, bringing an externally prepared gaseous reducing agent into intimate contact with the thus-heated material and thereby reducing the compounds of tin to metallic tin without fusion of the non-metallic constituents of said material and roducing a prodnot in which the re uced metallic tin is more or less scattered throughout said non-metallic constituents, and subjecting said product to appropriate subsequent treatment for the segregation and separation therefrom of the metallic tin.

6. A metallurgical process for the treatment of tin ores, concentrates, or other appropriate tin-containing material, which comprises heating the tin-containing material in afinely divided condition to a temperature of from 550 C. to 900 (3., bringing an externally prepared gaseous reduc ing agent into intimate contact with the thus-heated material and thereby reducing the compounds of tin to metallic tin without fusion of the non-metallic constituents of said material and producing a product of finely divided physical condition 1n which the reduced metallic tin is more or less scattered throughout said non-metallic constituents, and subjecting said product to appropriate subsequent treatment for the se ation and separation therefrom of the metal ic tin.

7. A metallurgical process for the treatment of tin ores, concentrates, or other appropriate tin-containing material, which comprises subjecting the material to the action of a gaseous reducin agent together with a small amount of ch orine or hydrochloric acid at a temperature of from 550 C. to 900 C.

8. The method of recovering tin from sulfide ores, which comprises roasting the ore, and subjecting the roasted ore to the action of hydrogen at an elevated temperature, small amounts of chlorine or h drochloric acid being added to promote t e removal of any remaining sulfur.

9. The method of recovering tin from oxidized ores or concentrates containing sulfur, which com rises subjectin the ore to the action of hy rogen and smal amounts of chlorine or hydrochloric acid at a temperature of about 600 to 850 C.

10. The method of recovering tin from oxidized ores, concentrates, or other appropriate tin-containing material, which comprises subjecting the tin-containing material to the action of hydrogen at an elevated temperature, and separating the reduced tin from the resulting roduct by centrifugal action at a sutficient y high temperature to melt the tin.

In testimony whereof I aflix no signature.

COLIN FINK. 

